Granted, at this point, it should be pretty obvious I guess, but I'm just looking for ways to absolutely confirm what the issue is, as I've become quite weary of this car. I'm honestly trying to get rid of it at this point, and I swear every time I do that some new issue pops up, and I'd rather sell a working car.

Anyway, it appears to be overheating as the temperature gauge now sits around half in about 90* F weather while driving at highway/freeway speeds, and can creep a bit higher especially when slowing down.

I did a coolant flush, replaced the thermostat, it's not burning/leaking any coolant whatsoever, when warm the fan clutch does offer resistance, and the belts on the pump appear to be fine and it's spinning.

Obviously, doesn't seem like much else it could be, but I've spent money this way before to find out another test and then discover it wasn't the part I replaced.

So! Does anyone have any advice as to a definitive test to check that it is indeed the water pump? Thanks in advance.

 

Here is a cooling trouble shooting guide from Aaron Cake:

http://www.aaroncake.net/RX-7/cooling.htm

Hopefully this will help you figure out the issue.

 

Yeah, that's what I was going by I'm afraid. It's possible that it's the radiator I suppose (I'll have to try the heat test, missed that one), but I'm pretty sure it's less than 3 years old, and there's no apparent damage and no leaks.

Which leaves the water pump. If I was keeping the car I'd take the time to tap the housing and add a proper sensor and gauge (DIGITAL, man I love hard numbers), but sadly no.

 

Hmm.... have you checked the engine for coolant leaks after it reaches normal temperature?

What I did was looking at both the upper and lower coolant hose after driving to see if there are any coolant shooting out or dripping down to the undertray, and that's how I detected there was major leaking involved.

When my car had cooling issues, aside from the radiator needing to be replaced, the thermostat housing cover had a crack, one of the hose and a connector hose underneath the radiator was leaking (these two hoses are hard to see unless you look from underneath the car).

Those were all replaced and then my car was fine. (Installed a Koyo radiator at the same time too)

 

Key points to be concerned with:

Is airflow blocked by something? Is the AC condenser or radiator so dirty that air can't flow through it?

Do you have the plastic under tray and radiator shroud?

Is the thermostat a Mazda OEM thermostat?

Is the alternator belt PROPERLY tensioned?

 

Just keep in mind... You hit 240 °F and your engine is done.

 

Yep, no leaks at all that I can find. I'll check again looking underneath the car but when I flushed my coolant I was pretty diligent about checking hoses and keeping on eye on the levels in the overflow and under the cap.

And I found out the 'fun way' that it seems to be keeping pressure just fine, turns out the car wasn't fully cool once when I popped off the radiator cap.

I don't know the first one, but it seems unlikely, it's pretty clean under there in general, but I will double check tomorrow. The plastic under tray and radiator shroud are both there and in good condition.

The thermostat is not a Mazda OEM thermostat, but neither was the last one which I have no proof of having actually malfunctioned as I just replaced it because it was cheap and might have been the problem, and it had been on there for a year previously. It was replaced with the same kind that had gone into it, and to the best of my knowledge, the thermostat I replaced originally was also the same kind. So I don't really see why that's an issue? I know they have the little bit on top that I'm guessing is different than other cars, but I've never actually examined other thermostats.

I guess I can't say 100 percent that the alternator belt is properly tensioned, and I don't believe I have the tools to do this, but it offers the same resistance to pressure as it did previous to this issue? That's the best answer I can give for that, unfortunately.

Indeed, which is why when I noticed the gauge creeping around/above half I pulled over and let it cool down a bit.

Also I was notified that the day I was driving it was actually 100* and possibly a bit over, I might take it for a drive tonight to see how it fares in cooler temperatures.

 

The fun way that you explain of checking pressure in the cooling system is of no value. Even a totally shot system will still pop when hot. You need to go to autozone and borrow a pressure testing kit. And yes you need a genuine mazda thermostat.

 

Can anyone explain why you need a 'genuine' one? Especially considering, like I said, it ran fine without? And I've seen plenty of evidence around the forums that other people run non genuine ones without? I haven't seen an actual reason why, just people saying 'yes, you do'.

Also, if there was a pressure leak, wouldn't it be leaking coolant somewhere?

 

Mazda OEM thermostat ensures proper flow and control of the cooling system, it opens and closes according to the coolant sensor so that the engine would not overheat. I would say put an OEM thermostat on and see if that solves the issue?

Another question I just had in mind.... How's the oil pressure and oil level for the car? Cause 1/3 of the engine's cooling is done by the oil cooler, so if the oil cooler or the oil cooler lines have issues, that may lead to overheating as well.

 

I just want to point out that half way up the gauge on an S4 is not exactly overheating. That is about 200F (per my Rtek), which is when the thermostat is fully open (cracks at 182F). If it goes beyond the point that the thermostat controls it to, then you're overheating. But that's not to say that half way at freeway speeds indicates the system is 100% fine. At freeway speeds (even in HOT weather), I'd say I never see more than 1/3 on the gauge, which is somewhere around 190F.

1/4: ~ 180F
1/2: ~ 200F
3/4: ~ 220F
4/4: Goodbye coolant seals

 

Mazda OEM part defines one single part known to function properly. Generics includes oem-level replacements to cheap knock-offs that stick or open at the wrong temperature. Which one did you get? You can test it with a thermometer and boiling water, but it's just easier to not have to worry.

Slow drips are easier to find with a pressure tester and a cold engine. You don't have the fan blowing in your face, coolant won't drip and evaporate before you can see it and you can remove as many parts as you want in order to see stuff. It'll also help rule out a minor coolant seal leak that could be causing overheating issues.

 

https://www.rx7club.com/2nd-generati...7/#post5131205

2nd Gen RX-7 New Owner Information

There is substantial evidence that non OEM thermostats, specifically Stant, will cause an engine overheat. Even brand new ones.

There are several write ups that can help with your overheating issues. Aaron's is very well thought out and gives you a methodical approach to fixing it.

I Overheated My Car. What Now?

 

every cooling system has a bypass port or hose, so that the water pump can pump water around with the thermostat closed. the rotaries have a simple hole below the thermostat that lets the water just go thru the hole and back into the block when the thermostat is closed.

so the factory (which is made by NTC), thermostat has a little flap at the bottom to close the bypass hole when the thermostat opens.

the aftermarket thermostats either don't have this, or it doesn't work, this results in coolant being able to skip going thru the radiator, and just circle around the block. this is also why just removing the thermostat is bad, because the bypass is open

the competition water pumps, simply had the bypass welded shut, and no thermostat.

so the moral? buy an NTC thermostat, and skip the stant

 

Never buy cheap parts for your 7, .only thing ill get for my car from autozone is vacuum/fuelhoses, Ngk spaplugs/wires and brake related items.

Never really want to get anything but oem for most things, they aren't engineered for rotary engines and many parts have bad fitment.

Mazdatrix.com is pricey but they have most little parts you'll need.

Unless you can find another place with Mazda parts at cheaper prices think my Waterpump was like $75 for my s4 na.

I also went ahead and got new oem radiator and tstat neck caps.

If your car is having cooling problems after you replace all that, it could very well be a bad clutch fan(unless u are using an e fan)

 

just wanna point out if you guys need cheaper Mazda parts, you can try Mazmart. as long as Mazda still have the part they can get it for you, and 99% of the time their price WILL BE CHEAPER than Mazdatrix and most if not ALL dealerships across the country, they have tight relationships with Mazda. Just trying to point this out.

I don't work for them, but I have been buying stuff from him for years for my 8, and they have been extremely helpful.

 

I have measured the OEM stats and the aftermarket stats. Most of the aftermarkets do have the piece to close off the bypass port.

Most of the aftermarket stats do not have the jiggle pin, so air pockets have more trouble moving out of the engine back into the radiator.

All the aftermarket stats have a substantially smaller diameter opening for the coolant to flow to the radiator. Some of them are as much as 1/3 smaller diameter. I believe this is caused by using a generic stamped part. It is made to be cheap and sturdy. The smaller opening absolutely restricts the flow of coolant to the radiator under full open conditions.

Go OEM only on this part.